# Drill Feed Rate Calculator

Drill feed rate calculator for CNC and manual drilling. Enter drill diameter and RPM (or let it compute RPM from material SFM) to get feed rate in IPM, IPR, and mm/min.

## What this calculates

A drill feed rate calculator turns spindle RPM and feed per revolution into the feed rate you program on a mill, lathe, or drill press. Feed per revolution scales with drill diameter in a predictable way (typically 0.015 IPR per inch of drill in steel), and the calculator applies that scaling automatically. Output is given in IPR, IPM, and mm/min so the same numbers work on any CNC control.

## Inputs

- **Drill Diameter** (in) — min 0.001 — Drill bit cutting diameter.
- **Spindle RPM Source** — options: Enter RPM directly, Compute from diameter and SFM — Compute mode uses the Machinery's Handbook SFM for the chosen material.
- **Spindle RPM** (RPM) — min 1 — Used when RPM Source = Enter directly.
- **Workpiece Material** — options: Aluminum, Mild steel / 1018, Alloy steel / 4140, Stainless steel, Cast iron, Brass, Bronze, Copper, Titanium, Tool steel, Plastic — Sets the default feed per revolution and (in compute mode) the target SFM.
- **Drill Material** — options: HSS, Solid carbide — Used only for the SFM lookup in compute mode.
- **Feed per Revolution Override** (in/rev) — min 0 — Leave at 0 to use the material default (feed scaled to diameter). Enter a specific IPR to override.
- **Hole Depth** (in) — min 0 — Used to estimate cycle time at the calculated feed rate.

## Outputs

- **Feed Rate (IPM)** (in/min) — Linear feed = RPM x IPR.
- **Feed per Revolution** (in/rev) — IPR, scaled to drill diameter by default.
- **Feed Rate (metric)** (mm/min) — Feed rate in mm/min = IPM x 25.4.
- **Spindle RPM Used** (RPM) — Direct entry or computed from SFM.
- **Cycle Time at Depth** (s) — Approximate time = hole depth / feed rate.

## Details

Drill feed rate formula

  - Feed rate (IPM) = RPM x IPR where IPR is the feed per revolution.

  - IPR scales with drill diameter: typical values are 0.018 IPR per inch of diameter in mild steel, 0.020 in aluminum, 0.012 in stainless, 0.010 in titanium.

  - RPM = (SFM x 12) / (pi x D) in compute mode, where D is drill diameter in inches and SFM is the target cutting speed.

For a 1/4 inch HSS drill in mild steel: SFM = 80, so RPM = (80 x 12) / (pi x 0.25) = 1,222 RPM. IPR = 0.018 x 0.25 = 0.0045. Feed rate = 1,222 x 0.0045 = 5.5 IPM. Convert to metric: 5.5 x 25.4 = 139.7 mm/min.

Drill feed per revolution (IPR) reference

Feed per revolution in a drill scales roughly linearly with diameter. These values are IPR per inch of drill diameter.

  
    MaterialIPR per inch of drill DExample (1/4" drill)
  
  
    Aluminum0.0200.0050
    Mild steel (1018)0.0180.0045
    Alloy steel (4140)0.0140.0035
    Stainless steel0.0120.0030
    Cast iron0.0200.0050
    Titanium0.0100.0025
    Plastic0.0250.0063
  

Drill feed rate vs milling feed rate

Milling feed is chip-load-per-tooth times flutes times RPM. Drilling feed is feed-per-revolution times RPM, with no flute multiplier because the two cutting lips of a drill share one chip per revolution. That is why a drill feed rate calculator and a mill feed rate calculator produce different IPM for the same SFM: a 1/4 inch HSS drill at 1,222 RPM and 0.0045 IPR feeds at 5.5 IPM, while a 1/4 inch HSS end mill at 1,222 RPM and 0.002 IPT chip load with 4 flutes feeds at 9.8 IPM.

Adjusting feed for hole depth

For shallow holes (up to about 3x drill diameter) use the full calculated feed. For deep holes over 5x diameter, drop feed 20-30 percent because the chip has further to travel out of the flutes. Add pecks at about 1x diameter intervals to break the chip and clear it from the hole. For blind holes, add a 0.5-1.0 second dwell at depth before the retract to clean up the bottom.

Feed rate overrides

Use the override field to enter a specific IPR (for example, from a tooling vendor's data sheet). A few common cases where the table default is wrong: spade drills (lower IPR than twist drills), step drills (use the largest step diameter), carbide tipped drills in hard materials (specific IPR from the manufacturer), and gun drills (very low IPR with high pressure coolant).

## Frequently Asked Questions

**Q: How do I calculate drill feed rate?**

A: Feed rate (IPM) = RPM x IPR, where IPR is feed per revolution. For a 1/4 inch HSS drill in mild steel at 1,222 RPM with 0.0045 IPR, feed rate = 1,222 x 0.0045 = 5.5 IPM. This drill feed rate calculator derives IPR from drill diameter and material when you do not specify one.

**Q: What IPR should I use for drilling mild steel?**

A: About 0.018 IPR per inch of drill diameter. A 1/4 inch drill = 0.0045 IPR. A 1/2 inch drill = 0.009 IPR. A 3/4 inch drill = 0.0135 IPR. Feed rate in IPM = RPM x IPR, so bigger drills feed faster at the same SFM even though RPM is lower.

**Q: Why does drill IPR scale with diameter?**

A: A bigger drill has more room for chips in each flute, so it can take a thicker chip without plugging. Scaling IPR with diameter keeps chip thickness and cutting force roughly constant across drill sizes. If you held IPR constant, small drills would chip the cutting edge and big drills would dawdle.

**Q: How do I convert drill feed rate to metric?**

A: Feed rate in mm/min = IPM x 25.4. A 5.5 IPM drilling feed = 139.7 mm/min. IPR x 25.4 = mm/rev. A 0.0045 IPR feed = 0.114 mm/rev. This calculator returns both units automatically.

**Q: Should I drop drill feed rate for deep holes?**

A: Yes, drop about 20-30 percent below the calculator value when hole depth exceeds 5x drill diameter, and add peck cycles at about 1x diameter intervals. Deep holes plug with chips if you run full feed. In titanium or stainless, drop even further and use a peck depth closer to 0.5x drill diameter.

**Q: What is the difference between IPR and IPM for drilling?**

A: IPR is feed per spindle revolution, which sets chip thickness per revolution. IPM is feed per minute, which sets the travel rate the CNC commands. They are linked by IPM = RPM x IPR. CNC drill cycles (G81, G83) usually program IPM, but some controls accept IPR directly under G95.

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Source: https://vastcalc.com/calculators/physics/drill-feed-rate
Category: Physics
Last updated: 2026-04-08